Golf ball manufacturers have been using ultraviolet irradiation to cure coatings and inks used on outer surfaces of golf balls for many years. For example, the use of a ultraviolet curable top coat is believed to eliminate the need for the traditionally used primer coat because of increased adhesion to the golf ball cover, as disclosed in U.S. Pat. No. 5,827,134. In addition, this patent teaches the ultraviolet curing of a partially neutralized copolymers of ethylene and acrylic acid to form a cured golf ball cover layer. U.S. Pat. Nos. 6,013,330 and 6,099,415 discuss the use of ultraviolet radiation curable ink to print an indicia or logo on outer surfaces of golf balls. The coating and/or inks typically used with such treatment are extremely thin, however, i.e., less than about 0.001 inches.
Radiation treatment has also been employed to seal the needle puncture holes necessary to insert liquid into fluid-filled golf ball cores. U.S. Pat. Nos. 5,922,252 and 5,624,332 teach methods of plugging the puncture holes with materials that solidify upon application of ultraviolet light radiation.
The list of additives in various golf ball layer compositions, particular covers, has recently included ultraviolet light absorbers and/or ultraviolet light stabilizers. For example, because the polyurethanes used to make the covers of golf balls typically contain an aromatic component, e.g., an aromatic diisocyanate, polyol or polyamine, they are susceptible to discoloration upon exposure to light, particularly ultraviolet light. To slow down this discoloration, light and UV stabilizers, e.g., TINUVIN® 770, 765 and 328, are added to these aromatic polymeric materials.
In addition, the recent trend toward light stable cover materials has introduced durability and adhesion issues, particularly between the inner cover layer and a polyurethane outer cover layer. For example, the inner components of most commercially available polyurethane golf balls undergo a surface treatment, e.g., corona discharge/silane dipping, to overcome the adhesion problems. The surface treatment, however, adds cost and time to the manufacturing process.
U.S. Pat. No. 6,265,476 discusses radiation curable binder compositions for optical fibers, glass substrates, and sewing threads with enhanced durability and elongation. The properties of such compositions would be beneficial in golf ball inner components, however, there is no such development in this area for golf ball manufacturing.
Thus, a need exists in the golf ball art for a material that is easily processed, but one that has good durability as a golf ball layer. In addition, a need exists for improved layer materials that reduce or eliminate adhesion problems with materials used in other inner layers, cover layers, and coating layers. Moreover, a need exists in the art for a method to use this material to form highly durable, resilient golf balls tailorable to have virtually any combination of feel and spin rate.